Moderately retarded, institutionalized retarded adults are trained in the acquisition of miniature language systems. These are comprised of laboratory tasks in which the subjects must learn the semantic meaning of a set of new signs and then use this knowledge to mediate the learning of a novel syntactic arrangement of the signs. The syntactic rules or ordering of signs corresponds to a classification of the signs by their semantic meaning. The creative or generative aspect of language systems is tested by requiring subjects to syntactically order signs whose meaning are known but whose syntactic ordering has not been directly trained. The research conducted in this program uses these miniature language systems to study the effects on linguistic acquisition of such variables as the nature of the semantic meanings, the kinds of syntactic orderings and subject variables such as mental age and IQ.